Refrigerating machine oil, and composition for refrigerating machine

ABSTRACT

The present invention relates to a refrigerator oil containing a specified amount of a polyvinyl ether-based compound (A) containing a structural unit (a1) having a methoxy group in a side chain thereof and a specified amount of a polyvinyl ether-based compound (B) containing a structural unit (b2) of a specified structure; a refrigerator oil composition containing the refrigerator oil; and a production method the refrigerator oil.

TECHNICAL FIELD

The present invention relates to a refrigerator oil, a refrigerator oilcomposition containing the refrigerator oil, and a method of producingthe refrigerator oil.

BACKGROUND ART

In general, a compression-type refrigerator has a structure such thatnot only it is configured of at least a compressor, a condenser, anexpansion mechanism (such as an expansion valve), an evaporator, and soon, but also a mixture of a refrigerant and a refrigerator oil(hereinafter also referred to as “refrigerator oil composition”) iscirculated within a closed system.

As the refrigerant which is used for compression-type refrigerators,fluorinated hydrocarbon compounds with a low environmental load havebeen being used in place of conventionally frequently usedhydrochlorofluorocarbon (HCFC). As the fluorinated hydrocarboncompounds, saturated fluorinated hydrocarbon compounds (HFC:Hydro-Fluoro-Carbon), such as 1,1,1,2-tetrafluoroethane (R134a),difluoromethane (R32), and a mixture of difluoromethane andpentafluoroethane (R410A), are frequently used. In recent years,investigations regarding refrigerants containing R32 having a lowerglobal warming potential is advanced.

In addition, use of unsaturated fluorinated hydrocarbon compounds (HFO:Hydro-Fluoro-Olefin) having a low global warming potential, such as1,3,3,3-tetrafluoropropene (R1234ze) and 2,3,3,3-tetrafluoropropene(R1234yf), is also investigated.

For example, as the refrigerator oil which is used for a refrigerantcontaining a saturated fluorinated hydrocarbon, those obtained byblending a polyvinyl ether compound, such as polyethyl vinyl ether andan ethyl vinyl ether/isobutyl vinyl ether copolymer, with an additive,such as an antioxidant, an acid scavenger, and an extreme pressureagent, are known (see, for example, PTLs 1 and 2).

In addition, for example, as the refrigerator oil which is used for arefrigerant containing an unsaturated fluorinated hydrocarbon, thosecontaining, as a base oil, a polyol ester and a polyoxyalkylene glycolin a mass ratio of 10/90 to 98/2 are known (see, for example, PTL 3).

CITATION LIST Patent Literature

PTL 1: JP 2013-14672 A

PTL 2: JP 2013-14673 A

PTL 3: JP 2015-54928 A

SUMMARY OF INVENTION Technical Problem

In compression-type refrigerators having the aforementioned structure,depending upon the kind of an apparatus, in general, the temperaturebecomes high within the compressor, whereas it becomes low within thecondenser, and therefore, the refrigerant and the lubricating oil arerequired to be circulated within this system without causing phaseseparation in a wide temperature range of from low temperatures to hightemperatures.

For that reason, in the compression-type refrigerators, the developmentof a refrigerator oil having excellent compatibility with therefrigerant over a wider temperature range of from low temperatures tohigh temperatures is demanded.

Furthermore, the refrigerator oil to be used is also required to havefavorable storage stability under a low temperature condition.

In view of the foregoing problems, the present invention has been made.A problem of the present invention is to provide a refrigerator oilwhich is not only excellent in compatibility with a refrigerant but alsofavorable in storage stability.

Solution to Problem

The present inventors made extensive and intensive investigations. As aresult, it has been found that a refrigerator oil containing a polyvinylether-based compound (A) containing a specified amount of a structuralunit (a1) having a methoxy group in a side chain thereof and a polyvinylether-based compound (B) containing a specified amount of a structuralunit (b2) of a specified structure is capable of solving theaforementioned problem. The present invention has been accomplished on abasis of such a finding. Specifically, in accordance with the respectiveembodiments of the present invention, the following [1] to [4] areprovided.

-   [1] A refrigerator oil containing:

a polyvinyl ether-based compound (A) containing a structural unit (a1)having a methoxy group in a side chain thereof in an amount of 50 mol %or more on a basis of 100 mol % of the whole amount of structural unitsexcluding a terminal structural unit in a molecular structure thereof;and

a polyvinyl ether-based compound (B) containing a structural unit (b2)represented by the following general formula (2) in an amount of morethan 50 mol % on a basis of 100 mol % of the whole amount of structuralunits excluding a terminal structural unit in a molecular structurethereof:

wherein R⁵, R⁶, and R⁷ each independently represent a hydrogen atom or ahydrocarbon group having 1 or more and 8 or less carbon atoms; R⁸represents a divalent hydrocarbon group having 2 or more and 10 or lesscarbon atoms; n represents a number of 0 or more and 10 or less; and R⁹represents a hydrocarbon group having 2 or more and 10 or less carbonatoms.

-   [2] A refrigerator oil composition containing the refrigerator oil    as set forth in the above [1] and a refrigerant.-   [3] A method of producing a refrigerator oil, including blending at    least

a polyvinyl ether-based compound (A) containing a structural unit (a1)having a methoxy group in a side chain thereof in an amount of 50 mol %or more on a basis of 100 mol % of the whole amount of structural unitsexcluding a terminal structural unit in a molecular structure thereof;and

a polyvinyl ether-based compound (B) containing a structural unit (b2)represented by the following general formula (2) in an amount of morethan 50 mol % on a basis of 100 mol % of the whole amount of structuralunits excluding a terminal structural unit in a molecular structurethereof, to obtain a refrigerator oil:

wherein R⁵, R⁶, and R⁷ each independently represent a hydrogen atom or ahydrocarbon group having 1 or more and 8 or less carbon atoms; R⁸represents a divalent hydrocarbon group having 2 or more and 10 or lesscarbon atoms; n represents a number of 0 or more and 10 or less; and R⁹represents a hydrocarbon group having 2 or more and 10 or less carbonatoms.

-   [4] A refrigerator having the refrigerator oil as set forth in the    above [1] or the refrigerator oil composition as set forth in the    above [2] filled therein.

Advantageous Effects of Invention

It is possible to provide a refrigerator oil which is not only excellentin compatibility with a refrigerant but also favorable in storagestability.

Description of Embodiments

[Refrigerator Oil]

A refrigerator oil according to one embodiment of the present invention(hereinafter referred to simply as “refrigerator oil”) contains, as acomponent (A), a polyvinyl ether-based compound (A) containing astructural unit (a1) having a methoxy group in a side chain thereof inan amount of 50 mol % or more on a basis of 100 mol % of the wholeamount of structural units excluding a terminal structural unit in amolecular structure thereof; and, as component (B), a polyvinylether-based compound (B) containing a structural unit (b2) representedby the following general formula (2) in an amount of more than 50 mol %on a basis of 100 mol % of the whole amount of structural unitsexcluding a terminal structural unit in a molecular structure thereof.

In the general formula (2), R⁵, R⁶, and R⁷ each independently representa hydrogen atom or a hydrocarbon group having 1 or more and 8 or lesscarbon atoms; R⁸ represents a divalent hydrocarbon group having 2 ormore and 10 or less carbon atoms; n represents a number of 0 or more and10 or less; and R⁹ represents a hydrocarbon group having 2 or more and10 or less carbon atoms.

In view of the fact that the aforementioned refrigerator oil containsboth the component (A) and the component (B), it is not only excellentin compatibility with a refrigerant but also favorable in storagestability.

The respective components which are contained in the refrigerator oilare hereunder described.

<Polyvinyl Ether-Based Compound (A)>

The polyvinyl ether-based compound (A) which is used in the refrigeratoroil is a compound having a polyvinyl ether structure and contains astructural unit (a1) having a methoxy group in a side chain thereof(hereinafter also referred to simply as “component (A)”). The component(A) contains the structural unit (a1) in an amount of 50 mol % or moreon a basis of 100 mol % of the whole amount of structural unitsexcluding a terminal structural unit of the component (A) as mentionedlater, in a molecular structure of the component (A).

In view of the fact that the refrigerator oil contains the component(A), even under any of a low-temperature environment and ahigh-temperature environment, it is excellent in compatibility with arefrigerant and hardly causes separation of the refrigerator oil and therefrigerant from each other.

In the refrigerator oil, the component (A) may be contained alone, ormay be contained in combination of two or more thereof.

(Structural Unit (a1))

The structural unit (a1) which the polyvinyl ether-based compound (A)contains in a molecular structure thereof is one having a methoxy groupin a side chain thereof, and preferably one represented by the followinggeneral formula (1).

In the general formula (1), R¹, R², and R³ each independently representa hydrogen atom or a hydrocarbon group having 1 or more and 8 or lesscarbon atoms; R⁴ represents a divalent hydrocarbon group having 2 ormore and 10 or less carbon atoms; and m represents a number of 0 or moreand 10 or less.

The carbon number of the hydrocarbon group having 1 or more and 8 orless carbon atoms, which may be selected as R¹ to R³, is preferably 1 ormore and 6 or less, more preferably 1 or more and 4 or less, and stillmore preferably 1 or 2.

Examples of the hydrocarbon group having 1 or more and 8 or less carbonatoms include alkyl groups, such as a methyl group, an ethyl group, an-propyl group, an isopropyl group, a n-butyl group, an isobutyl group,a sec-butyl group, a tert-butyl group, various pentyl groups, varioushexyl groups, various heptyl groups, and various octyl groups;cycloalkyl groups, such as a cyclopentyl group, a cyclohexyl group,various methylcyclohexyl groups, various ethylcyclohexyl groups, andvarious dimethylcyclohexyl groups; aryl groups, such as a phenyl group,various methylphenyl groups, various ethylphenyl groups, and variousdimethylphenyl groups; and arylalkyl groups, such as a benzyl group,various phenylethyl groups, and various methylbenzyl groups.

Above all, it is preferred that all of R¹ to R³ are a hydrogen atom oran alkyl group, and it is more preferred that all of R¹ to R³ are ahydrogen atom.

R¹'s, R²'s, or R³'s in the general formula (1) may be the same ordifferent in each structural unit. That is, the polyvinyl ether-basedcompound (A) may include a copolymer including the structural unitswhere some or all of R¹ to R³ are different in each structural unit.

The carbon number of the divalent hydrocarbon group having 2 or more and10 or less carbon atoms, which may be selected as R⁴, is preferably 2 ormore and 6 or less, and more preferably 2 or more and 4 or less.

Examples of the divalent hydrocarbon group which may be selected as R⁴include alkylene groups, such as an ethylene group, a phenylethylenegroup, a 1,2-propylene group, a 2-phenyl-1,2-propylene group, a1,3-propylene group, various butylene groups, various pentylene groups,various hexylene groups, various heptylene groups, various octylenegroups, various nonylene groups, and various decylene groups; divalentalicyclic hydrocarbon groups, such as a cyclohexylene group, amethylcyclohexylene group, an ethylcyclohexylene group, adimethylcyclohexylene group, and a propylcyclohexylene group; divalentaromatic hydrocarbon groups, such as various phenylene groups, variousmethylphenylene groups, various ethylphenylene groups, variousdimethylphenylene groups, and various naphthylene groups; divalent alkylaromatic hydrocarbon groups having a monovalent binding site in each ofan alkyl group moiety and an aromatic moiety of an alkyl aromatichydrocarbon, such as toluene and ethylbenzene; and divalent alkylaromatic hydrocarbon groups having a binding site in an alkyl groupmoiety of a polyalkyl aromatic hydrocarbon, such as xylene anddiethylbenzene.

Of these, R⁴ is preferably an alkylene group, and more preferably analkylene group having 2 or more and 4 or less carbon atoms.

m represents a number of 0 or more and 10 or less, preferably 0 or moreand 3 or less, more preferably 0 or more and 2 or less, still morepreferably 0 or 1, and yet still more preferably 0. In the case where mis 0, the carbon atom with which R³ is bound and the oxygen atom of OCH₃are bound with each other. In addition, in the case where m is 2 ormore, plural R⁴'s may be the same as or different from each other.

The component (A) may contain other structural unit than the structuralunit (a1).

However, the content of the structural unit (a1) is 50 mol % or more and100 mol % or less, preferably 60 mol % or more and 100 mol % or less,more preferably 70 mol % or more and 100 mol % or less, still morepreferably 80 mol % or more and 100 mol % or less, and yet still morepreferably 100 mol % on a basis of the whole amount (100 mol %) of thestructural units excluding a terminal structural unit in a molecularstructure terminal of the component (A) as mentioned later.

[Structural Unit (a1-1)]

The structural unit (a1) is preferably a structural unit (a1-1)represented by the following general formula (1-1).

In view of the fact that the component (A) contains the structural unit(a1-1), the compatibility of the resulting refrigerator oil with therefrigerant is more improved. In addition, the production of thecomponent (A) becomes easy.

In the general formula (1-1), R¹, R², and R³ each independentlyrepresent a hydrogen atom or a hydrocarbon group having 1 or more and 8or less carbon atoms.

In the general formula (1-1), R¹, R², and R³ are the same as R¹, R², andR³ in the general formula (1) as mentioned above, and therefore, theirexplanations are omitted.

The content of the structural unit (a1-1) is preferably 50 mol % or moreand 100 mol % or less, more preferably 70 mol % or more and 100 mol % orless, still more preferably 80 mol % or more and 100 mol % or less, andyet still more preferably 100 mol % on a basis of the whole amount (100mol %) of the structural unit (a1) which is contained in the component(A).

[Structural Unit (a1-2)]

The structural unit (a1) is more preferably a structural unit (a1-2)represented by the following general formula (1-2).

In view of the fact that the component (A) contains the structural unit(a1-2) represented by the general formula (1-2), the compatibility ofthe resulting refrigerator oil with the refrigerant is still moreimproved. In addition, the production of the component (A) becomeseasier.

The content of the structural unit (a1-2) represented by the generalformula (1-2) is preferably 50 mol % or more and 100 mol % or less, morepreferably 70 mol % or more and 100 mol % or less, still more preferably80 mol % or more and 100 mol % or less, and yet still more preferably100 mol % on a basis of 100 mol % of the whole amount of the structuralunit (a1) which is contained in the component (A).

(Structural Unit of Molecular Terminal of Polyvinyl Ether-Based Compound(A))

The terminal moiety of the molecular structure of the polyvinylether-based compound (A) may be represented by a monovalent groupderived from, for example, a saturated hydrocarbon, an ether, analcohol, a ketone, an amide, nitrile, etc. (hereinafter also referred toas “terminal structural unit”).

In one embodiment of the present invention, it is preferred that atleast one of the terminal structural units of the component (A) is aterminal structural unit (a11-1) represented by the following generalformula (11-1).

In the general formula (11-1), R¹¹, R¹², and R¹³ each independentlyrepresent a hydrogen atom or a hydrocarbon group having 1 or more and 8or less carbon atoms. The carbon number which the foregoing hydrocarbongroup having 1 or more and 8 or less carbon atoms has is preferably 1 ormore and 6 or less, more preferably 1 or more and 4 or less, and stillmore preferably 1 or 2.

R¹⁴ represents a divalent hydrocarbon group having 2 or more and 10 orless carbon atoms. The carbon number of the divalent hydrocarbon grouphaving 2 or more and 10 or less carbon atoms, which may be selected asR¹⁴, is preferably 2 or more and 6 or less, and more preferably 2 ormore and 4 or less.

p1 represents a number of 0 or more and 10 or less, preferably 0 or moreand 3 or less, more preferably 0 or more and 2 or less, still morepreferably 0 or 1, and yet still more preferably 0. In the case where p1is 0, the oxygen atom of OR¹⁵ and the carbon atom with which R¹³ isbound are bound with each other. In addition, in the case where p1 is 2or more, plural R¹⁴'s may be the same as or different from each other.

R¹⁵ represents a hydrocarbon group having 1 or more and 10 or lesscarbon atoms. The carbon number which the foregoing hydrocarbon grouphaving 1 or more and 10 or less carbon atoms has is preferably 1 or moreand 8 or less, more preferably 1 or more and 6 or less, still morepreferably 1 or more and 4 or less, yet still more preferably 1 or 2,and even yet still more preferably 1.

* represents a binding site to other structural unit than the terminalstructural units, such as the structural unit (a1).

Furthermore, in one embodiment of the present invention, one of theterminal structural units of the component (A) is the terminalstructural unit (a11-1) represented by the general formula (11-1), andthe other is preferably any of a terminal structural unit (a11-2)represented by the following general formula (11-2), a terminalstructural unit (a11-3) represented by the following general formula(11-3), and a terminal structural unit (a11-4) represented by thefollowing general formula (11-4), or a terminal structural unit havingan olefinically unsaturated bond, and more preferably a terminalstructural unit (a11-2) represented by the following general formula(11-2).

In the general formula (11-2), R^(11a), R^(12a), and R^(13a) eachindependently represent a hydrogen atom or a hydrocarbon group having 1or more and 8 or less carbon atoms. The carbon number which theforegoing hydrocarbon group having 1 or more and 8 or less carbon atomshas is preferably 1 or more and 6 or less, more preferably 1 or more and4 or less, and still more preferably 1 or 2.

R^(14a) represents a divalent hydrocarbon group having 2 or more and 10or less carbon atoms. The carbon number of the divalent hydrocarbongroup having 2 or more and 10 or less carbon atoms, which may beselected as R^(14a), is preferably 2 or more and 6 or less, and morepreferably 2 or more and 4 or less.

p2 represents a number of 0 or more and 10 or less, preferably 0 or moreand 3 or less, more preferably 0 or more and 2 or less, still morepreferably 0 or 1, and yet still more preferably 0. In the case where p2is 0, (R^(14a)O)₀ represents a single bond. In addition, in the casewhere p2 is 2 or more, plural R^(14a)'s may be the same as or differentfrom each other.

R^(15a) represents a hydrocarbon group having 1 or more and 10 or lesscarbon atoms. The carbon number which the hydrocarbon group having 1 ormore and 10 or less carbon atoms and being capable of being selected asR^(15a) has is preferably 1 or more and 8 or less, more preferably 1 ormore and 6 or less, still more preferably 1 or more and 4 or less, yetstill more preferably 1 or 2, and even yet still more preferably 1.

* represents a binding site to other structural unit than the terminalstructural units, such as the structural unit (a1).

In the general formula (11-3), R^(11b), R^(12b), and R^(13b) eachindependently represent a hydrogen atom or a hydrocarbon group having 1or more and 8 or less carbon atoms. The carbon number which theforegoing hydrocarbon group having 1 or more and 8 or less carbon atomshas is preferably 1 or more and 6 or less, more preferably 1 or more and4 or less, and still more preferably 1 or 2.

R^(14b) and R^(16b) each independently represent a divalent hydrocarbongroup having 2 or more and 10 or less carbon atoms. The carbon number ofthe divalent hydrocarbon group having 2 or more and 10 or less carbonatoms, which may be selected as R^(14b) and R^(16b), respectively, ispreferably 2 or more and 6 or less, and more preferably 2 or more and 4or less.

p3 and p4 each independently represents a number of 0 or more and 10 orless, preferably 0 or more and 3 or less, more preferably 0 or more and2 or less, still more preferably 0 or 1, and yet still more preferably0. In the case where p3 is 0, (R^(14b)O)₀ represents a single bond. Inaddition, in the case where p4 is 0, (R^(16b)O)₀ represents a singlebond. In addition, in the case where p3 is 2 or more, plural R^(14b)'smay be the same as or different from each other. In addition, in thecase where p4 is 2 or more, plural R^(16b)'s may be the same as ordifferent from each other.

R^(15b) and R^(17b) each independently represent a hydrocarbon grouphaving 1 or more and 10 or less carbon atoms. The carbon number of thehydrocarbon group having 1 or more and 10 or less carbon atoms, whichmay be selected as R^(15b) and R^(17b), respectively, is preferably 1 ormore and 8 or less, more preferably 1 or more and 6 or less, still morepreferably 1 or more and 4 or less, yet still more preferably 1 or 2,and even yet still more preferably 1.

* represents a binding site to other structural unit than the terminalstructural units, such as the structural unit (a1).

In the general formula (11-4), R^(11c), R^(12c), and R^(13c) eachindependently represent a hydrogen atom or a hydrocarbon group having 1or more and 8 or less carbon atoms. The carbon number which theforegoing hydrocarbon group having 1 or more and 8 or less carbon atomshas is preferably 1 or more and 6 or less, more preferably 1 or more and4 or less, and still more preferably 1 or 2.

* represents a binding site to other structural unit than the terminalstructural units, such as the structural unit (a1).

In the aforementioned general formulae (11-1), (11-2), (11-3), and(11-4), examples of the hydrocarbon group having 1 or more and 8 or lesscarbon atoms, which may be selected as R¹¹ to R¹³, R^(11a) to R^(13a),R^(11b) to R^(13b), and R^(11c) to R^(13c), respectively, include thesame hydrocarbon groups as the hydrocarbon group having 1 or more and 8or less carbon atoms, which may be selected as R¹ to R³ in the generalformula (1). In addition, suitable embodiments which may be selected asR¹¹ to R¹³, R^(11a) to R^(13a), R^(11b) to R^(13b), and R^(11c) toR^(13c), respectively, are the same as the suitable embodiments whichmay be selected as R¹ to R³ in the general formula (1).

Examples of the divalent hydrocarbon group having 2 or more and 10 orless carbon atoms, which may be selected as R¹⁴, R^(14a), R^(14b), andR^(16b), respectively, include the same divalent hydrocarbon groups asthe divalent hydrocarbon group having 2 or more and 10 or less carbonatoms, which may be selected as R⁴ in the general formula (1). Inaddition, suitable embodiments which may be selected as R¹⁴, R^(14a),R^(14b), and R^(16b), respectively, are the same as the suitableembodiments which may be selected as R⁴ in the general formula (1).

Examples of the hydrocarbon group, which may be selected as R¹⁵,R^(15a), R^(15b), and R^(17b)), respectively, include, in addition tothe same groups as the hydrocarbon group having 1 or more and 8 or lesscarbon atoms, which may be selected as R¹ to R³ in the aforementionedgeneral formula (1), alkyl groups, such as various nonyl groups andvarious decyl groups; cycloalkyl groups, such as variouspropylcyclohexyl groups and various trimethylcyclohexyl groups; arylgroups, such as various propylphenyl groups, various trimethylphenylgroups, various butylphenyl groups, and various naphthyl groups; andarylalkyl groups, such as various phenylpropyl groups and variousphenylbutyl groups.

Of these, R¹⁵, R^(15a), R^(15b), and R^(17b) are each preferably analkyl group, more preferably an alkyl group having 1 or more and 4 orless carbon atoms, still more preferably an alkyl group having 1 or 2carbon atoms, and yet still more preferably a methyl group.

(Synthesis Method of Polyvinyl Ether-Based Compound (A))

A synthesis method of the polyvinyl ether-based compound (A) is notparticularly limited, and there is exemplified a method in which using araw material monomer capable of forming the structural unit (a1) andoptionally, other raw material monomer (for example, a raw materialmonomer capable of forming a structural unit (b2) as mentioned later),the synthesis is performed by various means of polymerization (e.g.,radical polymerization, cationic polymerization, and radiationpolymerization).

Examples of the raw material monomer capable of forming the structuralunit (a1) include a vinyl ether-based monomer represented by thefollowing general formula (I).

In the general formula (I), R¹, R², R³, R⁴, and m are the same asdefined for R¹, R², R³, R⁴, and m in the general formula (1), andsuitable embodiments thereof are also the same.

As the synthesis method of the component (A), from the viewpoint ofobtaining the component (A) having a desired kinematic viscosity, amethod in which the raw material monomer is added in the system in thepresence of a polymerization catalyst and a polymerization initiator,thereby advancing the polymerization reaction is preferred.

Examples of the polymerization catalyst include a Lewis acid, a Brønstedacid, and an organometallic compound. Of these, a Lewis acid ispreferred.

Examples of the Lewis acid include boron trifluoride, aluminumtrichloride, aluminum tribromide, tin tetrachloride, zinc dichloride,and ferric chloride, with boron trifluoride being preferred.

Examples of the Brønsted acid include hydrofluoric acid, hydrochloricacid, hydrobromic acid, hydroiodic acid, nitric acid, sulfuric acid,trichloroacetic acid, and trifluoroacetic acid.

Examples of the organometallic compound include diethylaluminumchloride, ethylaluminum chloride, and diethylzinc.

Examples of the polymerization initiator include water, an alcohol, aphenol, an acetal, and an adduct between a vinyl ether and a carboxylicacid. These may be used either alone or in combination of two or morethereof. The terminal moiety of the resulting component (A), namely theterminal structural unit is formed according to the kind of such apolymerization initiator.

Examples of the alcohol include saturated aliphatic alcohols having 1 ormore and 20 or less carbon atoms, such as methanol, ethanol, propanol,isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, variouspentanols, various hexanols, various heptanols, and various octanols;unsaturated aliphatic alcohols having 3 or more and 10 or less carbonatoms, such as allyl alcohol; and ether bound oxygen-containing alcoholshaving 14 or less carbon atoms, such as an ethylene glycol monoalkylether and an ethylene glycol monoaryl ether.

Examples of the phenol include phenol and various cresols.

Examples of the acetal include acetaldehyde dimethyl acetal,acetaldehyde diethyl acetal, acetaldehyde methylethyl acetal, andacetaldehyde bis(methoxyethyl) acetal.

Examples of the adduct between of a vinyl ether and a carboxylic acidinclude adducts between a vinyl ether and acetic acid, propionic acid,n-butyric acid, isobutyric acid, 3,5,5-trimethylcaproic acid, etc.

At a polymerization initiating terminal of the resulting component (A),in the case of using water, an alcohol, or a phenol, hydrogen is bound,and in the case of using an acetal used, one resulting from eliminationof one of the alkoxy groups from the acetal is bound. In addition, inthe case of using an adduct between a vinyl ether and a carboxylic acid,one resulting from elimination of an alkyl carbonyloxy group derivedfrom the carboxylic acid moiety from the adduct of the vinyl ether andthe carboxylic acid is bound.

Meanwhile, in the case of using water, an alcohol, a phenol, or anacetal, the stopped terminal of the component (A) becomes an acetal, anolefin, or an aldehyde. In addition, in the case of an adduct between avinyl ether and a carboxylic acid, the stopped terminal of the component(A) becomes a carboxylic acid ester of a hemiacetal, and when hydrolyzedin the presence of an acid, it becomes an aldehyde.

Depending upon the kind of the raw material monomer or polymerizationinitiator to be used, the polymerization reaction is performed at atemperature of preferably −80° C. or higher and 150° C. or lower, andmore preferably 0° C. or higher and 100° C. or lower, and it ispreferred to terminate the polymerization reaction for from 10 secondsto 10 hours after commencement of the reaction.

The polymerization reaction is typically performed in the presence of asolvent. Although the solvent to be used is not particularly limited solong as it is not only able to dissolve a necessary amount of thereaction raw material therein but also inert to the polymerizationreaction, examples thereof include hydrocarbon-based solvents, such ashexane, benzene, and toluene; and ether-based solvents, such as ethylether, 1,2-dimethoxyethane, and tetrahydrofuran.

After the polymerization reaction, in the case where the resultingpolymer has an unsaturated bond, an acetal, and an aldehyde, in order tocovert these into a saturated bond and an ether, it is preferred tofurther perform a hydrogenation treatment. The hydrogenation treatmentcan be performed in the presence of a hydrogenation catalyst at areaction temperature of preferably 10° C. or higher and 250° C. orlower, and more preferably 50° C. or higher and 200° C. or lower whileintroducing a hydrogen gas preferably at a hydrogen pressure of 0.1 MPaGor more and 10 MPaG or lower, and more preferably at a hydrogen pressureof 1 MPaG or more and 6 MPaG or lower.

Examples of the hydrogenation catalyst include metal catalysts, such asa nickel-based catalyst, a platinum-based catalyst, a palladium-basedcatalyst, and a ruthenium-based catalyst, and catalysts having such ametal catalyst supported on alumina, diatomaceous earth, etc.;Raney-type catalysts; and the like can be used.

<Polyvinyl Ether-Based Compound (B)>

The polyvinyl ether-based compound (B) which is used in the refrigeratoroil is a compound having a polyvinyl ether structure and contains astructural unit (b2) represented by the following general formula (2)(hereinafter also referred to simply as “component (B)”). The component(B) contains the structural unit (b2) in an amount of more than 50 mol %on a basis of 100 mol % of the whole amount of structural unitsexcluding a terminal structural unit of the component (B) as mentionedlater, in a molecular structure of the component (B).

In view of the fact that the refrigerator oil contains the component(B), the storage stability, in particular, the storage stability under alow-temperature environment is improved, and generation of cloudiness ofthe refrigerator oil at the time of storage is suppressed.

In the refrigerator oil, the component (B) may be contained alone, ormay be contained in combination of two or more thereof.

(Structural Unit (b2))

The structural unit (b2) which the polyvinyl ether-based compound (B)contains in a molecular structure thereof is one having a hydrocarbongroup other than a methoxy group in a side chain thereof and is onerepresented by the following general formula (2).

In the formula (2), R⁵, R⁶, and R⁷ each independently represent ahydrogen atom or a hydrocarbon group having 1 or more and 8 or lesscarbon atoms; R⁸ represents a divalent hydrocarbon group having 2 ormore and 10 or less carbon atoms; n represents a number of 0 or more and10 or less; and R⁹ represents a hydrocarbon group having 2 or more and10 or less carbon atoms.

In the general formula (2), examples of the hydrocarbon group having 1or more and 8 or less carbon atoms, which may be selected as R⁵ to R⁷,respectively, include the same hydrocarbon groups as the hydrocarbongroup having 1 or more and 8 or less carbon atoms, which may be selectedas R¹ to R³ in the general formula (1). In addition, suitableembodiments which may be selected as R⁵ to R⁷, respectively, are thesame as the suitable embodiments which may be selected as R¹ to R³ inthe general formula (1).

Examples of the divalent hydrocarbon group having 2 or more and 10 orless carbon atoms, which may be selected as R⁸, include the samehydrocarbon groups as the divalent hydrocarbon group having 2 or moreand 10 or less carbon atoms, which may be selected as R⁴ in the generalformula (1). In addition, suitable embodiments which may be selected asR⁸ are the same as the suitable embodiments which may be selected as R⁴in the general formula (1).

n represents a number of 0 or more and 10 or less, preferably 0 or moreand 3 or less, more preferably 0 or more and 2 or less, still morepreferably 0 or 1, and yet still more preferably 0. In the case where nis 0, the carbon atom with which R⁷ is bound and the oxygen atom of OR⁹are bound with each other. In addition, in the case where n is 2 ormore, plural R⁸'s may be the same as or different from each other.

R⁹ represents a hydrocarbon group having 2 or more and 10 or less carbonatoms. The carbon number which the hydrocarbon group having 2 or moreand 10 or less carbon atoms and being capable of being selected as R⁹has is preferably 2 or more and 8 or less, more preferably 2 or more and6 or less, still more preferably 2 or more and 4 or less, yet still morepreferably 2 or 3, and even yet still more preferably 2.

Examples of the hydrocarbon group which may be selected as R⁹ includehydrocarbon groups having 2 or more carbon atoms among the hydrocarbongroups as exemplified as the hydrocarbon group having 1 or more and 10or less carbon atoms, which may be selected as R¹⁵ in the aforementionedgeneral formula (11-1). Above all, R⁹ is preferably an alkyl group, morepreferably an alkyl group having 2 or more and 4 or less carbon atoms,and still more preferably an ethyl group.

The component (B) may contain other structural unit than the structuralunit (b2).

However, the content of the structural unit (b2) is more than 50 mol %and 100 mol % or less, preferably 60 mol % or more and 100 mol % orless, more preferably 70 mol % or more and 100 mol % or less, still morepreferably 80 mol % or more and 100 mol % or less, and yet still morepreferably 100 mol % on a basis of 100 mol % of the whole amount of thestructural units excluding a terminal structural unit in a molecularstructure terminal of the component (B) as mentioned later in amolecular structure of the component (B).

[Structural Unit (b2-1)]

The structural unit (b2) is preferably a structural unit (b2-1)represented by the following general formula (2-1).

In view of the fact that the component (B) contains the structural unit(b2-1), the storage stability of the resulting refrigerator oil, inparticular, the storage stability under a low-temperature environment ismore improved. In addition, the production of the component (B) becomeseasy.

In the general formula (2-1), R⁵, R⁶, and R⁷ each independentlyrepresent a hydrogen atom or a hydrocarbon group having 1 or more and 8or less carbon atoms; R⁸ represents a divalent hydrocarbon group having2 or more and 10 or less carbon atoms; and n represents a number of 0 ormore and 10 or less.

In the general formula (2-1), R⁵, R⁶, R⁷, R⁸, and n are the same as R⁵,R⁶, R⁷, R⁸, and n in the general formula (2) as mentioned above, andtherefore, their explanations are omitted.

The content of the structural unit (b2-1) is preferably 50 mol % or moreand 100 mol % or less, more preferably 70 mol % or more and 100 mol % orless, still more preferably 80 mol % or more and 100 mol % or less, andyet still more preferably 100 mol % on a basis of the whole amount (100mol %) of the structural unit (b2) which is contained in the component(B).

[Structural Unit (b2-2)]

The structural unit (b2) is more preferably a structural unit (b2-2)represented by the following general formula (2-2).

In view of the fact that the component (B) contains the structural unit(b2-2), the storage stability of the resulting refrigerator oil, inparticular, the storage stability under a low-temperature environment isstill more improved. In addition, the production of the component (B)becomes easier.

In the general formula (2-2), R⁵, R⁶, and R⁷ each independentlyrepresent a hydrogen atom or a hydrocarbon group having 1 or more and 8or less carbon atoms.

In the general formula (2-2), R⁵, R⁶, and R⁷ are the same as R⁵, R⁶, andR⁷ in the general formula (2) as mentioned above, and therefore, theirexplanations are omitted.

The content of the structural unit (b2-2) is preferably 50 mol % or moreand 100 mol % or less, more preferably 70 mol % or more and 100 mol % orless, still more preferably 80 mol % or more and 100 mol % or less, andyet still more preferably 100 mol % on a basis of the whole amount (100mol %) of the structural unit (b2) which is contained in the component(B).

[Structural Unit (b2-3)]

The structural unit (b2) is still more preferably a structural unit(b2-3) represented by the following general formula (2-3).

In view of the fact that the component (B) contains the structural unit(b2-3), the storage stability of the resulting refrigerator oil, inparticular, the storage stability under a low-temperature environment isyet still more improved. In addition, the production of the component(B) becomes yet still easier.

The content of the structural unit (b2-3) is preferably 50 mol % or moreand 100 mol % or less, more preferably 70 mol % or more and 100 mol % orless, still more preferably 80 mol % or more and 100 mol % or less, andyet still more preferably 100 mol % on a basis of the whole amount (100mol %) of the structural unit (b2) which is contained in the component(B).

(Structural Unit of Molecular Terminal of Polyvinyl Ether-Based Compound(B))

As the terminal moiety of the molecular structure of the polyvinylether-based compound (B), the same structural unit as the terminalmoiety of the molecular structure of the component (A) as mentionedabove is exemplified, and its suitable embodiment is also the sameexcept for the following point, and therefore, the explanations thereofare omitted.

With respect to the terminal moiety of the molecular structure of thepolyvinyl ether-based compound (B), as for suitable embodiments whichmay be selected as R¹⁵, R^(15a), R^(15b), and R^(17b), respectively, inthe aforementioned general formulae (11-1), (11-2), (11-3), and (11-4),among those mentioned above, an alkyl group is preferred, an alkyl grouphaving 1 or more and 4 or less carbon atoms is more preferred, and anethyl group is still more preferred.

(Synthesis Method of Polyvinyl Ether-Based Compound (B))

A synthesis method of the polyvinyl ether-based compound (B) is notparticularly limited, and there is exemplified a method in which using araw material monomer capable of forming the structural unit (b2) andoptionally, other raw material (for example, a raw material monomercapable of forming the structural unit (a1)), the synthesis is performedby various means of polymerization (e.g., radical polymerization,cationic polymerization, and radiation polymerization).

Examples of the raw material monomer capable of forming the structuralunit (b2) include a vinyl ether-based monomer represented by thefollowing general formula (II).

In the general formula (II), R⁵, R⁶, R⁷, R⁸, R⁹, and n are the same asdefined for R⁵, R⁶, R⁷, R⁸, R⁹, and n in the general formula (2), andsuitable embodiments thereof are also the same.

As for a synthesis method of the component (B), the same method as thesynthesis method of the component (A) as mentioned above can be adopted,except for using, as the raw material monomer, the vinyl ether-basedmonomer represented by the general formula (II), and a suitableembodiment of each of conditions is also the same, and therefore, theexplanation thereof is omitted.

In the refrigerator oil, a content ratio [(A)/(B)] of the component (A)and the component (B) is preferably 10/90 or more and 90/10 or less interms of a mass ratio. When the content ratio [(A)/(B)] is satisfiedwith the foregoing range, the compatibility with a refrigerant and thestorage stability of the resulting refrigerator oil can be moreimproved. From such a viewpoint, the content ratio [(A)/(B)] is morepreferably 20/80 or more, still more preferably 35/65 or more, yet stillmore preferably 45/55 or more, and even yet still more preferably 55/45or more, and it is more preferably 85/15 or less, still more preferably80/20 or less, and yet still more preferably 75/25 or less, in terms ofa mass ratio.

In the refrigerator oil, from the viewpoint of obtaining a refrigeratoroil which is not only excellent in compatibility with a refrigerant butalso favorable in storage stability, the total content of the component(A) and the component (B) is preferably 70.0% by mass or more, morepreferably 75.0% by mass or more, still more preferably 80.0% by mass ormore, yet still more preferably 85.0% by mass or more, and even yetstill more preferably 90.0% by mass or more, and it is 100% by mass orless, preferably 99.7% by mass or less, more preferably 99.0% by mass orless, still more preferably 98.5% by mass or less, yet still morepreferably 98.0% by mass or less, and even yet still more preferably97.5% by mass or less, on a basis of the whole amount (100% by mass) ofthe refrigerator oil.

A kinematic viscosity at 40° C. of the mixture of the component (A) andthe component (B) (hereinafter also referred to simply as “40° C.kinematic viscosity ”) is preferably 1.0 mm²/s or more, more preferably10.0 mm²/s or more, still more preferably 20.0 mm²/s or more, yet stillmore preferably 30.0 mm²/s or more, and even yet still more preferably50.0 mm²/s or more from the viewpoint that leakage of the resultingrefrigerator oil from between members to be lubricated can be preventedfrom occurring. From the viewpoint of conservation of energy, the 40° C.kinematic viscosity of the mixture of the component (A) and thecomponent (B) is preferably 90.0 mm²/s or less, more preferably 80.0mm²/s or less, and still more preferably 75.0 mm²/s or less.

A viscosity index (VI) of the mixture of the component (A) and thecomponent (B) is preferably 55 or more, more preferably 60 or more,still more preferably 65 or more, and yet still more preferably 70 ormore from the viewpoint of lubricity. Although its upper limit is notparticularly limited, it is preferably 250 or less.

<Other Components>

The refrigerator oil may contain, in addition to the components (A) and(B), various additives, a mineral oil, and a synthetic oil other thanthe polyvinyl ether-based compounds (A) and (B) (hereinafter alsoreferred to as “other synthetic oil”), as mentioned later.

(Additives)

The refrigerator oil may further contain, in addition to the components(A) and (B), one or more of any various additives, such as anantioxidant (C) (hereinafter also referred to simply as “component(C)”), an acid scavenger (D) (hereinafter also referred to simply as“component (D)”), an extreme pressure agent (E) (hereinafter alsoreferred to simply as “component (E)”), an anti-foaming agent, an oilyagent, an oxygen scavenger, a metal deactivator, and a rust inhibitor.Of these, at least one selected from the group consisting of anantioxidant (C), an acid scavenger (D), and an extreme pressure agent(E) is preferably contained.

In the case where the refrigerator oil contains the component (C) or thecomponent (D), an increase of an acid number of the refrigerator oilunder a high-temperature environment can be prevented from occurring,and thermal stability of the refrigerator oil can be improved, andhence, such is preferred. In addition, in the case where therefrigerator oil contains both the component (C) and the component (D),the increase of an acid number can be more suppressed, and the thermalstability of the refrigerator oil can be more improved, and hence, suchis more preferred.

In the case where the refrigerator oil contains the component (E), wearresistance under a high-temperature environment becomes favorable, andlubricity can be more improved, and hence, such is preferred.

The antioxidant (C), the acid scavenger (D), the extreme pressure agent(E), and other additives are hereunder described in order.

(Antioxidant (C))

Examples of the antioxidant (C) include a phenol-based antioxidant andan amine-based antioxidant.

Examples of the phenol-based antioxidant include a monophenol-basedantioxidant and a polyphenol-based antioxidant.

Examples of the monophenol-based antioxidant include alkyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionates (examples of the alkyl groupinclude those having 4 to 20 carbon atoms, and preferably 8 to 18 carbonatoms), such as n-octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,6-methylheptyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, andn-octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;2,6-di-tert-butyl-4-alkylphenols (the alkyl group has 1 or more and 4 orless carbon atoms), such as 2,6-di-tert-butyl-4-methylphenol and2,6-di-tert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol, and2,6-di-tert-amyl-p-cresol.

Examples of the polyphenol-based antioxidant include4,4′-methylenebis(2, 6-di-tert-butylphenol),4,4′-bis(2,6-di-tert-butylphenol),4,4′-bis(2-methyl-6-tert-butylphenol),2,2′-methylenebis(4-ethyl-6-tert-butylphenol),2,2′-methylenebis(4-methyl-6-tert-butylphenol),4,4′-butylidenebis(3-methyl-6-tert-butylphenol),4,4′-isopropylidenebis(2,6-di-tert-butylphenol),2,2′-methylenebis(4-methyl-6-nonylphenol),2,2′-isobutylidenebis(4,6-dimethylphenol),2,2′-methylenebis(4-methyl-6-cyclohexylphenol),4,4′-thiobis(2-methyl-6-tert-butylphenol),4,4′-thiobis(3-methyl-6-tert-butylphenol),2,2′-thiobis(4-methyl-6-tert-butylphenol),bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide,bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide, andthiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

Examples of the amine-based antioxidant include dialkyl diphenylamines,such as 4,4′-dibutyl diphenylamine and 4,4′-dioctyl diphenylamine;phenyl-α-naphthylamines, such as an alkylphenyl-α-naphthylamine andphenyl-α-naphthylamine; and N,N′ -diphenyl-p-phenylenediamine.

As the antioxidant (C), a phenol-based antioxidant is preferred from theviewpoints that an increase of an acid number of the resultingrefrigerator oil is suppressed, and that oxidation stability at a hightemperature is more easily improved. In addition, among those mentionedabove, the phenol-based antioxidant is more preferably a2,6-di-tert-butyl-4-alkylphenol, and still more preferably2,6-di-tert-butyl-4-methylphenol.

The content of the component (C) in the refrigerator oil is preferably0.1% by mass or more, more preferably 0.2% by mass or more, and stillmore preferably 0.3% by mass or more on a basis of the whole amount ofthe refrigerator oil from the viewpoints that an increase of an acidnumber of the resulting refrigerator oil is suppressed, and thatoxidation stability at a high temperature is more easily improved. Theforegoing content is preferably 5.0% by mass or less, more preferably3.0% by mass or less, and still more preferably 1.0% by mass or lessfrom the viewpoint of making it easy to exhibit an effect correspondingto the content.

The component (C) may be used alone, or may be used in combination oftwo or more thereof.

(Acid Scavenger (D))

Examples of the acid scavenger (D) include an epoxy compound. Examplesof the epoxy compound include a glycidyl ether compound, cyclohexeneoxide, an α-olefin oxide, and epoxidized soybean oil. Of these, aglycidyl ether compound is preferred.

Examples of the glycidyl ether compound include an aliphatic monoalcoholhaving preferably 3 or more and 30 or less carbon atoms, more preferably4 or more and 24 or less carbon atoms, and still more preferably 6 ormore and 16 or less carbon atoms; an aliphatic polyhydric alcohol having3 or more and 30 or less carbon atoms, more preferably 4 or more and 24or less carbon atoms, and still more preferably 6 or more and 16 or lesscarbon atoms; and an aromatic compound-derived glycidyl ether containing1 or more hydroxy groups. Although the aliphatic monoalcohol or thealiphatic polyhydric alcohol may be linear, branched, or cyclic and maybe saturated or unsaturated, it is preferably a saturated aliphaticmonoalcohol.

In the case of an aliphatic polyhydric alcohol, or in the case of anaromatic compound containing two or more hydroxy groups, it is preferredthat all of the hydroxy groups are glycidyl etherified from theviewpoints of stability of the refrigerator oil and suppression of anincrease of a hydroxy value.

Examples of the glycidyl ether compound include phenyl glycidyl ether,an alkyl glycidyl ether, and an alkylene glycol glycidyl ether. Ofthese, a glycidyl ether derived from a linear, branched, or cyclicsaturated aliphatic monoalcohol having 6 or more and 16 or less carbonatoms (namely, an alkyl glycidyl ether in which an alkyl group thereofhas 6 or more and 16 or less carbon atoms) is more preferred from theviewpoints that an increase of an acid number of the resultingrefrigerator oil is suppressed, and that oxidation stability at a hightemperature is more easily improved. Examples of such a glycidyl etherinclude 2-ethylhexyl glycidyl ether, isononyl glycidyl ether, decylglycidyl ether, lauryl glycidyl ether, and myristyl glycidyl ether, with2-ethylhexyl glycidyl ether being still more preferred.

The content of the component (D) in the refrigerator oil is preferably0.1% by mass or more, more preferably 0.4% by mass or more, still morepreferably 0.8% by mass or more, and yet still more preferably 1.5% bymass or more on a basis of the whole amount of the refrigerator oil fromthe viewpoint of appropriately capturing an acid in the resultingrefrigerator oil and effectively suppressing the increase of an acidnumber, thereby making it easier to improve the oxidation stability at ahigh temperature. The foregoing content is preferably 10.0% by mass orless, more preferably 5.0% by mass or less, still more preferably 3.0%by mass or less, and yet still more preferably 2.5% by mass or less fromthe viewpoint of making it easy to exhibit an effect corresponding tothe content.

The component (D) may be used alone, or may be used in combination oftwo or more thereof.

As mentioned above, in view of the fact that the component (D) is usedin combination with the component (C), the increase of an acid number ofthe resulting refrigerator oil can be more suppressed.

(Extreme Pressure Agent (E))

Examples of the extreme pressure agent (E) include a phosphorus-basedextreme pressure agent. Examples of the phosphorus-based extremepressure agent include a phosphoric acid ester, a phosphorous acidester, an acidic phosphoric acid ester, an acidic phosphorous acidester, and amine salts thereof.

Examples of the phosphoric acid ester include a triaryl phosphate, atrialkyl phosphate, a monoalkyl diaryl phosphate, a dialkyl monoarylphosphate, and a trialkenyl phosphate. The “aryl” mentioned regardingthe component (E) is a concept including not only a functional groupcomposed of only an aromatic ring but also an alkylaryl and anarylalkyl.

Examples of the phosphoric acid ester include triaryl phosphates, suchas triphenyl phosphate, tricresyl phosphate, benzyl diphenyl phosphate,cresyl diphenyl phosphate, dicresyl phenyl phosphate, propylphenyldiphenyl phosphate, dipropylphenyl phosphate, ethylphenyl diphenylphosphate, diethylphenyl phenyl phosphate, triethylphenyl phosphate,tripropylphenyl phosphate, butylphenyl diphenyl phosphate, dibutylphenylphenyl phosphate, and tributylphenyl phosphate; alkyl phosphates, suchas tributyl phosphate, ethyldibutyl phosphate, trihexyl phosphate,tri(2-ethylhexyl) phosphate, tridecyl phosphate, trilauryl phosphate,trimyristyl phosphate, tripalmityl phosphate, and tristearyl phosphate;ethyl diphenyl phosphate, and trioleyl phosphate.

Examples of the acidic phosphoric acid include various alkyl acidphosphates and dialkyl acid phosphates.

Examples of the phosphorous acid ester include various trialkylphosphites, triaryl phosphites, monoalkyl diaryl phosphites, dialkylmonoaryl phosphites, and trialkenyl phosphites.

Examples of the acidic phosphorous acid ester include various dialkylhydrogen phosphites, dialkenyl hydrogen phosphites, and diaryl hydrogenphosphites.

The phosphorus-based extreme pressure agent may also be a sulfuratom-containing phosphoric acid ester, such as trithiophenyl phosphate,or the like. Examples of the amine salt include amine salts of an acidicphosphoric acid ester or an acidic phosphorous acid ester. The aminethat forms the amine salt may be a primary, secondary, or tertiaryamine.

Of those, the component (E) is preferably a phosphoric acid ester, andabove all, it is more preferably a triaryl phosphate, and still morepreferably tricresyl phosphate. In view of the fact that a triarylphosphate, such as tricresyl phosphate, is used, lubricity of theresulting refrigerator oil at a high temperature, or the like readilybecomes favorable. Examples of other preferred component (E) includetrithiophenyl phosphate, tri(nonylphenyl) phosphite, dioleyl hydrogenphosphite, and 2-ethylhexyl diphenyl phosphite.

The content of the component (E) in the refrigerator oil is preferably0.1% by mass or more, more preferably 0.3% by mass or more, still morepreferably 0.5% by mass or more, and yet still more preferably 0.7% bymass or more on a basis of the whole amount of the refrigerator oil fromthe viewpoint of improving the wear resistance of the resultingrefrigerator oil. The foregoing content is preferably 5.0% by mass orless, more preferably 3.0% by mass or less, still more preferably 2.5%by mass or less, and yet still more preferably 2.0% by mass or less fromthe viewpoint of making it easy to exhibit an effect corresponding tothe content.

When the refrigerator oil contains the extreme pressure agent (E), theacid number tends to increase. However, by jointly using the antioxidant(C) and the acid scavenger (D), it is possible to improve the wearresistance while suppressing an increase of the acid number to be causeddue to the extreme pressure agent (E).

In consequence, from the viewpoint of obtaining a refrigerator oil whichis excellent in thermal stability and excellent in a balance with thewear resistance, a refrigerator oil containing all of the component (C),the component (D), and the component (E) is preferred.

The refrigerator oil may also be a refrigerator oil composed of only thecomponent (A) and the component (B). In the case of a refrigerator oilcontaining these additives, a refrigerator oil composed of only thecomponent (A) and the component (B) as well as at least one selectedfrom the group consisting of the components (C) to (E) is preferred; arefrigerator oil composed of only the component (A) and the component(B) as well as at least two selected from the group consisting of thecomponents (C) to (E) is more preferred; and a refrigerator oil composedof only the component (A) and the component (B) as well as the component(C), the component (D), and the component (E) is still more preferred.

In the case of a refrigerator oil containing all of the component (C),the component (D), and the component (E), a preferred content of each ofthe components (A) to (E) is the same as mentioned above. That is, thetotal content of the polyvinyl ether compound (A) and the polyvinylether compound (B), the content of the antioxidant (C), the content ofthe acid scavenger (D), and the content of the extreme pressure agent(E) are each preferably

components (A) and (B) in total: 70% by mass or more and 99.7% by massor less,

component (C): 0.1% by mass or more and 5.0% by mass or less,

component (D): 0.1% by mass or more and 10.0% by mass or less, and

component (E): 0.1% by mass or more and 5.0% by mass or less, morepreferably

components (A) and (B) in total: 75% by mass or more and 99.0% by massor less,

component (C): 0.1% by mass or more and 3.0% by mass or less,

component (D): 0.4% by mass or more and 5.0% by mass or less, and

component (E): 0.3% by mass or more and 3.0% by mass or less, still morepreferably

components (A) and (B) in total: 80% by mass or more and 98.0% by massor less,

component (C): 0.2% by mass or more and 1.0% by mass or less,

component (D): 0.8% by mass or more and 3.0% by mass or less, and

component (E): 0.5% by mass or more and 2.5% by mass or less, and yetstill more preferably

components (A) and (B) in total: 85% by mass or more and 97.5% by massor less,

component (C): 0.3% by mass or more and 1.0% by mass or less,

component (D): 1.5% by mass or more and 2.5% by mass or less, and

component (E): 0.7% by mass or more and 2.0% by mass or less, on a basisof the whole amount of the refrigerator oil.

In the case where the refrigerator oil contains the components (C) to(E), preferred compounds of each of the components (C) to (E) are thesame as mentioned above.

That is, it is preferred that the antioxidant (C) is a phenol-basedantioxidant, the acid scavenger (D) is a glycidyl ether compound, andthe extreme pressure agent (E) is a phosphoric acid ester; it is morepreferred that the antioxidant (C) is a 2,6-di-tert-butyl-4-alkylphenol,the acid scavenger (D) is an alkyl glycidyl ether, and the extremepressure agent (E) is a triaryl phosphate; and it is still morepreferred that the antioxidant (C) is 2,6-di-tert-butyl-4-methylphenol,the acid scavenger (D) is 2-ethylhexyl glycidyl ether, and the extremepressure agent (E) is tricresyl phosphate.

[Other Additives]

The refrigerator oil may further contain, as additives, other additivesthan the components (C) to (E).

Examples of the other additive include an oxygen scavenger, an oilinessimprover, a copper deactivator, a rust inhibitor, and an anti-foamingagent. These additives may be used alone, or may be used in combinationof two or more thereof.

Examples of the oxygen scavenger include sulfur-containing aromaticcompounds, such as 4,4′-thiobis(3-methyl-6-tert-butylphenol), diphenylsulfide, dioctyl diphenyl sulfide, a dialkyl diphenylene sulfide,benzothiophene, dibenzothiophene, phenothiazine, benzothiapyran,thiapyran, thianthrene, dibenzothiapyran, and diphenylene disulfide;aliphatic unsaturated compounds, such as various olefins, dienes, andtrienes; and terpenes having a double bond in a molecular structurethereof.

Examples of the oiliness improver include aliphatic saturated orunsaturated monocarboxylic acids, such as stearic acid and oleic acid;polymerized fatty acids, such as a dimer acid and a hydrogenated dimeracid; hydroxy fatty acids, such as ricinoleic acid and 12-hydroxystearicacid; aliphatic saturated or unsaturated monoalcohols, such as laurylalcohol and oleyl alcohol; aliphatic saturated or unsaturatedmonoamines, such as stearylamine and oleylamine; aliphatic saturated orunsaturated monocarboxylic acid amides, such as lauric acid amide andoleic acid amide; and partial esters between a polyhydric alcohol, suchas glycerin and sorbitol, and an aliphatic saturated or unsaturatedmonocarboxylic acid.

Examples of the copper deactivator include an N-[N,N′-dialkyl (alkylgroup having 3 or more and 12 carbon atoms) aminomethyl]triazole.

Examples of the rust inhibitor include a metal sulfonate, an aliphaticamine, an organic sulfonic acid metal salt, an organic phosphoric acidmetal salt, an alkenyl succinic acid ester, and a polyhydric alcoholester.

Examples of the anti-foaming agent include silicone oils, such asdimethyl polysiloxane, and polymethacrylates.

In the case where the refrigerator oil contains such other additive, thecontent of each of the other additives is preferably 0.01% by mass ormore and 10% by mass or less, and more preferably 0.05% by mass or moreand 5% by mass or less on a basis of the whole amount (100% by mass) ofthe refrigerator oil.

(Mineral Oil and Other Synthetic Oil)

The refrigerator oil may contain various mineral oils; and syntheticoils other than the polyvinyl ether-based compounds (A) and (B)(hereinafter also referred to as “other synthetic oils”) within a rangewhere the effects of the present invention are not impaired.

Examples of the mineral oil include refined oils obtained by subjectinglubricating oil fractions obtained by atmospherically distilling aparaffinic, intermediate base, or naphthenic crude oil, orvacuum-distilling an atmospheric residual oil obtained byatmospherically distilling crude oil, to at least one of solventdeasphaltation, solvent extraction, hydrocracking, solvent dewaxing,catalytic dewaxing, and hydrorefining; oils produced by isomerizing amineral oil-based wax; and oils produced by isomerizing GTL WAX(gas-to-liquid) which is produced by the Fischer-Tropsch process, or thelike.

Examples of the other synthetic oil include synthetic oils, such as apolyvinyl ether-based compound not containing the structural units (a1)and (b2), a polyalkylene glycol-based compound, a copolymer of apoly(oxy)alkylene glycol or a monoether thereof and a polyvinyl ethernot containing the structural units (a1) and (b2), and a polyolester-based compound.

The mineral oil and other synthetic oil may be used either alone or incombination of two or more thereof.

As for the mineral oil and the other synthetic oil, ones having the same40° C. kinematic viscosity as the mixture of the polyvinyl ether-basedcompounds (A) and (B) may be used. The foregoing 40° C. kinematicviscosity is preferably 1.0 mm²/s or more, more preferably 10.0 mm²/s ormore, stull more preferably 20.0 mm²/s or more, yet still morepreferably 30.0 mm²/s or more, and even yet still more preferably 50.0mm²/s or more. It is preferably 90.0 mm²/s or less, more preferably 80.0mm²/s or less, and still more preferably 75.0 mm²/s or less.

The content of each of the mineral oil and the other synthetic oil ispreferably 0 part by mass or more and 30 parts by mass or less, morepreferably 0 part by mass or more and 20 parts by mass or less, stillmore preferably 0 part by mass or more and 10 parts by mass or less, andyet still more preferably 0 part by mass or more and 3 parts by mass orless based on 100 parts by mass of the total content of the component(A) and the component (B) from the viewpoint of providing a refrigeratoroil with excellent compatibility with a refrigerant.

<Characteristics of Refrigerator Oil>

The refrigerator oil is excellent in compatibility with a refrigerantunder any of a high-temperature environment and a low-temperatureenvironment.

A two-layer separation temperature at the high-temperature side of therefrigerator oil from the refrigerant is preferably 45° C. or higher,more preferably 50° C. or higher, still more preferably 55° C. orhigher, and yet still more preferably 60° C. or higher.

A two-layer separation temperature at the low-temperature side of therefrigerator oil from the refrigerant is preferably −5° C. or lower,more preferably −10° C. or lower, still more preferably −20° C. orlower, yet still more preferably −40° C. or lower, and even yet stillmore preferably −45° C. or lower.

In this specification, the foregoing “two-layer separation temperatureat the high-temperature side of the refrigerator oil from therefrigerant” and “two-layer separation temperature at thelow-temperature side of the refrigerator oil from the refrigerant” eachmean a value measured by the method described in the section of Examplesas mentioned later.

An acid number of the refrigerator oil as measured by the methoddescribed in the section of Examples as mentioned later is preferably1.50 or less, more preferably 1.10 or less, still more preferably 0.80or less, yet still more preferably 0.60 or less, even yet still morepreferably 0.30 or less, and even still more preferably 0.10 or lessfrom the viewpoint of improving the thermal stability.

A value of ring wear amount on the occasion of using the refrigeratoroil as measured by the method described in the section of Examples asmentioned later is preferably 2.0 or less, more preferably 1.5 or less,still more preferably 1.0 or less, yet still more preferably 0.8 orless, even yet still more preferably 0.7 or less, and even still morepreferably 0.6 or less from the viewpoint of improving the lubricity.

[Production Method of Refrigerator Oil]

A production method of the refrigerator oil according to one embodimentof the present invention is a method of producing a refrigerator oilincluding blending at least, as a component (A), a polyvinyl ether-basedcompound (A) containing a structural unit (a1) having a methoxy group ina side chain thereof and, as a component (B), a polyvinyl ether-basedcompound (B) containing a structural unit (b1) represented by thefollowing general formula (2).

In the general formula (2), R⁵, R⁶, and R⁷ each independently representa hydrogen atom or a hydrocarbon group having 1 or more and 8 or lesscarbon atoms; R⁸ represents a divalent hydrocarbon group having 2 ormore and 10 or less carbon atoms; n represents a number of 0 or more and10 or less; and R⁹ represents a hydrocarbon group having 2 or more and10 or less carbon atoms.

In the foregoing production method, in addition to the component (A) andthe component (B), at least one selected from the group consisting ofthe component (C), the component (D), and the component (E) may beblended, and the aforementioned other additives may be further blended.In addition, an oil other than the component (A) and the component (B)may be blended.

The detailed explanations regarding the component (A) and the component(B) as well as the components (C) to (E), the other additives, and theoil other than the component (A) and the component (B) are the same asthose mentioned above, and therefore, their explanations are omitted.

[Refrigerator Oil Composition]

The refrigerator oil is one to be used with a refrigerant upon beingmixed. In this specification, a mixture of the refrigerator oil and therefrigerant is referred to as “refrigerator oil composition”.

The refrigerator oil composition according to one embodiment of thepresent invention contains a refrigerant and the aforementionedrefrigerator oil.

<Refrigerant>

As the refrigerant, there is exemplified at least one selected from thegroup consisting of a fluorinated hydrocarbon, a hydrocarbon-basedrefrigerant that is a natural refrigerant, carbon dioxide, and ammonia.

A content ratio of the refrigerator oil and the refrigerant((refrigerator oil)/(refrigerant)) in the refrigerator oil compositionis preferably 1/99 or more and 99/1 or less, more preferably 1/99 ormore and 90/10 or less, still more preferably 5/95 or more and 70/30 orless, and yet still more preferably 5/95 or more and 60/40 or less interms of a mass ratio. By allowing the foregoing mass ratio of therefrigerator oil and the refrigerant to fall within the foregoing range,it is possible to obtain lubricity and suitable refrigerating capacityin a refrigerator.

(Fluorinated Hydrocarbon)

As the fluorinated hydrocarbon refrigerant, there is exemplified atleast one selected from the group consisting of a saturated fluorinatedhydrocarbon compound (HFC) and an unsaturated fluorinated hydrocarboncompound (HFO).

The saturated fluorinated hydrocarbon compound (HFC) is preferably afluoride of an alkane having 1 or more and 4 or less carbon atoms, morepreferably a fluoride of an alkane having 1 or more and 3 or less carbonatoms, and still more preferably a fluoride of an alkane having 1 or 2carbon atoms (methane or ethane). Examples of the fluoride of methane orethane include trifluoromethane (R23), difluoromethane (R32),1,1-difluoroethane (R152a), 1,1,1-trifluoroethane (R143a ),1,1,2-trifluoroethane (R143), 1,1,1,2-tetrafluoroethane (R134a),1,1,2,2-tetrafluoroethane (R134), and 1,1,1,2,2-pentafluoroethane(R125). Of these, at least one selected from the group consisting ofR32, R134a, and R125 is preferred; R32 and at least one selected fromthe group consisting of R134a and R125 are more preferred; and R32 isstill more preferred.

These saturated fluorinated hydrocarbon compounds may be used alone, ormay be used in combination of two or more thereof. Here, in the case ofusing a combination of two or more of the saturated fluorinatedhydrocarbon compounds, examples thereof include a mixed refrigerantresulting from mixing of two or more saturated fluorinated hydrocarboncompounds having 1 or more and 3 or less carbon atoms; and a mixedrefrigerant resulting from mixing of two or more saturated fluorinatedhydrocarbon compounds having 1 or more and 2 or less carbon atoms.

Examples of the mixed refrigerant include a mixture of R32 and R125(R410A); a mixture of R125, R143a , and R134a (R404A); a mixture of R32,R125, and R134a (e.g., R407A , R407C, and R407E); and a mixture of R125and R143a (R507A). The mixed refrigerant resulting from mixing of thesetwo or more refrigerants is preferably at least one selected from thegroup consisting of a mixture of R32, R125, and R134a, such as R407A ,R407C, and R407E; and a mixture of R32 and R125, such as R410A.

Examples of the unsaturated fluorinated hydrocarbon compound (HFO)include compounds having a carbon-carbon double bond, such as fluoridesof a linear or branched chain olefin having 2 or more and 6 or lesscarbon atoms; and a cyclic olefin having 4 or more and 6 or less carbonatoms.

More specifically, examples thereof include an ethylene having 1 or moreand 3 or less fluorine atoms introduced thereinto; a propene having 1 ormore and 5 or less fluorine atoms introduced thereinto; a butene having1 or more and 7 or less fluorine atoms introduced thereinto; a pentenehaving 1 or more and 9 or less fluorine atoms introduced thereinto; ahexene having 1 or more and 11 or less fluorine atoms introducedthereinto; a cyclobutene having 1 or more and 5 or less fluorine atomsintroduced thereinto; a cyclopentene having 1 or more and 7 or lessfluorine atoms introduced thereinto; and a cyclohexene having 1 or moreand 9 or less fluorine atoms introduced thereinto.

Of these unsaturated fluorinated hydrocarbon compounds, a fluoride of apropene is preferred; a propene having 3 or more and 5 or less fluorineatoms introduced thereinto is more preferred; and a propene having 4fluorine atoms introduced thereinto is still more preferred. As forother fluorides than the fluoride of a propene, a fluoride of ethyleneis preferred; an ethylene having 1 or more and 3 or less fluorine atomsintroduced thereinto is more preferred; and ethylene having 3 fluorineatoms introduced thereinto is still more preferred.

Suitable examples of the unsaturated fluorinated hydrocarbon refrigerantinclude 1,2,3,3,3-pentafluoropropene (R1225ye),2,3,3,3-tetrafluoropropene (R1234yf), 1,3,3,3-tetrafluoropropene(R1234ze), 1,2,3,3-tetrafluoropropene (R1234yz), 1,1,2-trifluoroethylene(R1123), and (Z)-1,1,1,4,4,4-hexafluoro-2-butene (R1336mzz(Z)). Ofthese, at least one selected from the group consisting of R1234yf,R1234ze, R1123, and R1336mzz (Z) is preferred.

These unsaturated fluorinated hydrocarbon compounds may be used alone,or may be used in combination of two or more thereof, and may also beused in combination with other refrigerant than the unsaturatedfluorinated hydrocarbon compound. Here, as for an example of the case ofusing the unsaturated fluorinated hydrocarbon compound in combinationwith other refrigerant than the unsaturated fluorinated hydrocarboncompound, a mixed refrigerant of a saturated fluorinated hydrocarboncompound and an unsaturated fluorinated hydrocarbon compound isexemplified, and a mixed refrigerant with R32 is preferably exemplified.Examples of the mixed refrigerant include a mixed refrigerant of R32 andR1234yf; a mixed refrigerant of R32 and R1123; a mixed refrigerant ofR32, R1234ze, and R152a; a mixed refrigerant of R32, R125, and R1234yf;a mixed refrigerant of R32, R125, R1234yf, and R134a; a mixedrefrigerant of R32, R125, R1234yf, R1234ze, and R134a; and a mixedrefrigerant of R32, R125, R1234yf, and R1234ze.

(Natural Refrigerant)

As the natural refrigerant, at least one selected from the groupconsisting of a hydrocarbon-based refrigerant, carbon dioxide (carbonicacid gas), and ammonia is exemplified, with a hydrocarbon-basedrefrigerant being preferred. These may be used alone, or may be used incombination of two or more thereof, or may be combined with otherrefrigerant than the natural refrigerant. Here, as an example of thecase using a combination with other refrigerant than the naturalrefrigerant, a mixed refrigerant with at least one selected from thegroup consisting of a saturated fluorinated hydrocarbon compound and anunsaturated fluorinated hydrocarbon compound is exemplified. Specificexamples of the mixed refrigerant include a mixed refrigerant of carbondioxide, HFO1234ze, and R134a (AC6, mixing ratio: 5.15/79.02/15.41).

The hydrocarbon-based refrigerant is preferably a hydrocarbon having 1or more and 8 or less carbon atoms, more preferably a hydrocarbon having1 or more and 5 or less carbon atoms, and still more preferably ahydrocarbon having 3 or more and 5 or less carbon atoms. When the carbonnumber is 8 or less, the boiling point of the refrigerant does notbecome excessively high, and hence, such is preferred as therefrigerant. As the hydrocarbon-based refrigerant, at least one selectedfrom the group consisting of methane, ethane, ethylene, propane (R290),cyclopropane, propylene, n-butane, isobutane (R600a), 2-methylbutane,n-pentane, isopentane, and cyclopentane/isobutane is exemplified, andthese may be used alone, or may be used in combination of two or morethereof. In addition, as the hydrocarbon-based refrigerant, only theaforementioned hydrocarbon may be used, or as mentioned above, it canalso be used a mixed refrigerant resulting from mixing of a fluorinatedhydrocarbon, such as R32 and R134a, or other refrigerant than thefluorinated hydrocarbon-based refrigerant, such as ammonia and carbondioxide.

Of these, the natural refrigerant is preferably at least one selectedfrom the group consisting of a hydrocarbon-based refrigerant, carbondioxide, and ammonia, more preferably a hydrocarbon-based refrigerant,and still more preferably propane (R290) or isobutane (R600a).

Such a natural refrigerant may also be used in combination with theaforementioned fluorinated hydrocarbon refrigerant.

The refrigerator oil that is one embodiment of the present invention isexcellent in compatibility with the refrigerant over a wide temperaturerange of from a low temperature to a high temperature, and therefore,the refrigerant is preferably a refrigerant containing difluoromethane(R32).

The refrigerant containing difluoromethane (R32) is more preferably R32alone or a mixture of R32 and at least one refrigerant selected from thegroup consisting of a fluorinated hydrocarbon refrigerant other thanR32, a hydrocarbon refrigerant, carbon dioxide, and ammonia, and stillmore preferably R32 alone. The refrigerant other than R32, which can beused in combination with R32, may be used alone or in combination of twoor more thereof.

In the case of using, as the refrigerant, a refrigerant containingdifluoromethane (R32), the content of R32 in the refrigerant containingdifluoromethane (R32) is preferably 10% by mass or more and 100% by massor less, more preferably 20% by mass or more and 100% by mass or less,still more preferably 30% by mass or more and 100% by mass or less, yetstill more preferably 50% by mass or more and 100% by mass or less, andeven yet still more preferably 70% by mass or more and 100% by mass orless on a basis of the whole amount (100% by mass) of the refrigerant.Above all, the refrigerant of R32 alone (100% by mass) is even stillmore preferred. That is, the aforementioned refrigerator oil can besuitably used as a refrigerator oil for refrigerant containing R32, andcan be more suitably used as a refrigerator oil for R32 refrigerant.

[Refrigerator]

The aforementioned refrigerator oil or refrigerator oil composition isfilled in the interior of the refrigerator and used.

The refrigerator is preferably a compression-type refrigerator, and morepreferably one having a refrigeration cycle including a compressor, acondenser, an expansion mechanism (e.g., an expansion valve), and anevaporator, or having a refrigeration cycle including a compressor, acondenser, an expansion mechanism, a dryer, and an evaporator.

The refrigerator is, for example, used for lubricating a sliding portionto be provided in a compressor, etc.

Although the sliding portion is not particularly limited, it ispreferred that any of the sliding portions contains a metal, such asiron, and it is preferably one to slide between a metal and a metal.

Although the refrigerator is applied to, for example, a car airconditioner, such as an open-type car air conditioner and an electriccar air conditioner, an air conditioner, a gas heat pump (GHP), arefrigeration system, such as a freezer, an icebox, a vending machine,and showcase, a hot water system, such as a water heater and a floorheater, and a heating system, it is preferably applied to an airconditioning application.

EXAMPLES

The present invention is hereunder more specifically described byreference to Examples, but it should be construed that the presentinvention is by no means limited by these Examples.

Respective physical properties of each component, each refrigerator oil,and each refrigerator oil composition were determined in the followingway.

[40° C. Kinematic Viscosity]

A 40° C. kinematic viscosity was measured in conformity with JISK2283:2000.

[Viscosity Index (VI)]

A kinematic viscosity at each of 40° C. and 100° C. was measured inconformity with JIS K2283:2000, and a viscosity index (VI) wascalculated.

[Compatibility Between Refrigerant and Refrigerator Oil]

A refrigerator oil composition containing 15% by mass of a refrigeratoroil and 85% by mass of a refrigerant on a basis of the whole amount ofthe refrigerator oil composition [refrigerator oil composition of(refrigerator oil)/(refrigerant)=15/85 (mass ratio)] was prepared.Difluoromethane (R32) was used as the refrigerant.

Using the resulting refrigerator oil composition, a two-layer separationtemperature at each of the low-temperature side and the high-temperatureside was measured by the following method.

<Two-Layer Separation Temperature at the High-Temperature Side>

The resulting refrigerator oil composition was charged in apressure-resistant glass ampule, and the ampule was connected to avacuum pipe and a refrigerant pipe and then subjected to vacuumdeaeration at room temperature (25° C.). Thereafter, the ampule wascooled with liquefied nitrogen, and a predetermined amount of arefrigerant was collected in the ampule via the refrigerant pipe,followed by sealing the ampule, thereby preparing an ampule having ameasurement sample enclosed therein.

Thereafter, the ampule was held in a thermostat; the ampule wasirradiated with a laser; the temperature of the thermostat was raisedfrom room temperature (25° C.) to 70° C. at a rate of 1° C./min whilemeasuring a light transmittance of the ampule; and a temperature of thethermostat when the light transmittance of the ampule became 50% of thelight transmittance of the ampule at room temperature was designated asa two-layer separation temperature at the high-temperature side of therefrigerator oil as a measurement object from the refrigerant. It isindicated that the higher the two-layer separation temperature at thehigh-temperature side of the refrigerator oil, the more excellent thecompatibility with a refrigerant at a high temperature.

A refrigerator oil composition which did not cause the two-layerseparation until at 70° C. is expressed as “70<” in the following Table1.

<Two-Layer Separation Temperature at the Low-Temperature Side>

A two-layer separation temperature at the low-temperature side wasmeasured adopting the same method as the measurement method of thetwo-layer separation temperature at the high-temperature side, exceptthat at the time of measurement, the ampule was cooled from roomtemperature at a rate of −1° C./min. It is indicated that the lower thetwo-layer separation temperature at the low-temperature side of therefrigerator oil, the more excellent the compatibility with arefrigerant at a low temperature.

A refrigerator oil composition which did not cause the two-layerseparation until at −50° C. is expressed as “−50>” in the followingTable 1.

[Storage Stability Test]

A refrigerator oil obtained in each of Examples and each of ComparativeExamples was stored in a 0.1-liter volume glass-made vessel and allowedto stand at −5° C. for 30 days, followed by observing an appearancethereof.

The obtained results are shown in Table 1.

Various descriptions in the table are as follows, in which “A” indicatesthat in the case of “transparent”, the storage stability is excellent,and “D” indicates that in the case of “separated”, the storage stabilityis inferior.

-   A: The state of “transparent”, expressing the state in which the    component (B) is uniformly dissolved in the component (A), and the    oil is “transparent”.-   B: The state of “slightly cloudy”, expressing the state in which    while the dissolution of the component (B) is more advanced than the    state of “cloudy”, the oil is extremely slightly opaque.-   C: The state of “cloudy”, expressing the state in which while the    component (B) is dissolved in the component (A), a part of the    component (B) is dispersed in the component (A), whereby the oil    becomes slightly opaque.-   D: The state of “separated”, expressing the state in which the    component (B) is not dissolved in the component (A), so that    light-liquid separation is caused.    [Thermal Stability Test: Autoclave Test]

The chemical stability between the refrigerator oil and the refrigerantwas evaluated in conformity with the method described in Appendix C ofJIS K2211:2009.

A stainless steel-made pressure-resistant vessel was charged with, ascatalysts, iron (Fe), copper (Cu), and aluminum (Al) [all having adiameter of 1.6 mm and a length of 300 mm] and sealed together with 30 gof the refrigerator oil and, as a refrigerant, 30 g of difluoromethane(R32) ((refrigerator oil)/(refrigerant) =30/30 (mass ratio), moisturecontent in the oil: 500 ppm by mass). Subsequently, the sealedpressure-resistant vessel was heated at 175° C. for 336 hours, and theacid number of the refrigerator oil was then measured in conformity withthe indicator titration method as prescribed in JIS K2501:2003.

The obtained results are shown in Table 2.

[Lubricity Test (Measurement of Ring Wear Amount)]

Using a sealed block-on-ring friction tester (LFW-1), a ring wear amountduring using each refrigerator oil was measured under a difluoromethane(R32) refrigerant environment under the following condition.

The obtained results are shown in Table 3.

Ring: FC250, block: SKH51

Rotation rate: 1,000 r/min, oil temperature: 80° C., refrigerantpressure: 0.4 MPa

During the running-in operation; load: 300 N, operation time: 1 minute

During the test; load: 500 N, operation time: 60 minutes

[Preparation Example: Preparation of Hydrogenation Catalyst]

A 2-liter volume SUS316L-made autoclave was charged with 6 g of a nickeldiatomaceous earth catalyst (a trade name: “N113”, manufactured by JGCCatalysts and Chemicals Ltd.) and 300 g of isooctane. The autoclave waspurged with nitrogen and subsequently purged with hydrogen. Thereafter,the temperature was raised while setting a hydrogen pressure to 3.0MPaG, and the autoclave was kept at 140° C. for 30 minutes and thencooled to room temperature.

After purging the autoclave with nitrogen, 10 g of acetaldehyde diethylacetal was added in the autoclave. The autoclave was again purged withnitrogen and subsequently purged with hydrogen. The temperature was thenraised to 130° C. while setting a hydrogen pressure to 3.0 MPaG, and theautoclave was kept at 130° C. for 30 minutes. On the occasion ofperforming this operation, the pressure within the autoclave wasincreased due to temperature rise, whereas the acetaldehyde diethylacetal reacted, whereby a reduction of the hydrogen pressure wasperceived. In the case where the hydrogen pressure was reduced andreached to 3.0 MPaG or less, hydrogen was injected into the autoclave,to regulate the hydrogen pressure such that it was kept at 3.0 MPaG.Thereafter, the autoclave was cooled to room temperature and thensubjected to depressurization. Subsequently, the autoclave was purgedwith nitrogen at atmospheric pressure, followed by deaeration.

[Synthesis Example 1: Synthesis of Polyvinyl Ether-Based Compound (A)]

A 1-liter glass-made flask installed with a stirrer was charged with 133g of toluene, 33.6 g of methanol as an initiator, and 0.2 g of a borontrifluoride diethyl ether complex. In addition, an Erlenmeyer flaskwhich had been prepared separately from the aforementioned 1-literglass-made flask was charged with 500 g of methyl vinyl ether as a rawmaterial monomer. The aforementioned methyl vinyl ether was supplied at5 mL/min with a pump while stirring the inside of the 1-liter glass-madeflask, and when 54 g of the methyl vinyl ether was supplied, the pumpwas once stopped. After confirming that the temperature within the1-liter glass-made flask was raised due to the reaction, the pump wasrebooted, and the rest of the methyl vinyl ether was supplied over 4hours. During supply of the methyl vinyl ether, the temperature wascontrolled with a water bath such that the temperature within the1-liter glass-made flask was 25° C. After completion of supply of theentirety of methyl vinyl ether, the stirring was further performed for 5minutes.

Subsequently, in the 1-liter glass-made flask, 10 g (mass ratio to a sumtotal of the initiator and the raw material monomer: 0.019) ofhydrotalcite (a trade name: “KYOWAAD (registered trademark) 500SH”,manufactured by Kyowa Chemical Industry Co., Ltd., a proportion ofparticles having a particle diameter of 500 μm or less: 100%, aproportion of particles having a particle diameter of 106 μm or less:94%, a proportion of particles having a particle diameter of 45 to 106μm: 56%) was added as an adsorbent and stirred at 25° C. for 1 hour,thereby adsorbing the boron trifluoride diethyl ether complex thereonto.Subsequently, the solution within the 1-liter glass-made flask wasfiltered to remove the adsorbent, and the solvent and the lightcomponent were removed with a rotary evaporator, to obtain a crudeproduct Aa.

The 2-liter volume SUS316L-made autoclave in which the hydrogenationcatalyst prepared in the Preparation Example had been charged wascharged with 120 g of the crude product Aa and 300 g of isooctane. Afterpurging the autoclave with hydrogen, the hydrogen pressure was kept at3.5 MPaG, the temperature was raised to 140° C. with stirring over 30minutes, and the contents were further allowed to react with each otherfor 3 hours while keeping at 140° C. After completion of the reaction,the resultant was cooled to room temperature, and the pressure wasreduced to atmospheric pressure. Filtration with a filter paper wasperformed, to remove the hydrogenation catalyst. The solvent, themoisture, and so on were removed under reduced pressure with a rotaryevaporator, to obtain a polyvinyl ether-based compound (A).

The resulting polyvinyl ether-based compound (A) was one containing 100mol % of the structural unit (a1-2) having a methoxy group, asrepresented by the general formula (1-2), on a basis of 100 mol % of thewhole amount of structural units excluding terminal structural units.

One of the terminal structural units is the structural unit (a11-1)represented by the general formula (11-1), and in the general formula(11-1), R¹¹, R¹², and R¹³ are each a hydrogen atom, R¹⁵ is a methylgroup, and p1 is 0.

Furthermore, the other terminal structural unit is the structural unit(a11-2) represented by the general formula (11-2), and in the generalformula (11-2), R^(11a), R^(12a), and R^(13a) are each a hydrogen atom,R^(15a) is a methyl group, and p2 is 0.

[Synthesis Example 2: Synthesis of Polyvinyl Ether-Based Compound (B)]

A 1-liter glass-made flask installed with a stirrer was charged with 106g of toluene, 24.3 g of ethanol as an initiator, and 0.2 g of a borontrifluoride diethyl ether complex. In addition, an Erlenmeyer flaskwhich had been prepared separately from the aforementioned 1-literglass-made flask was charged with 400 g of ethyl vinyl ether as a rawmaterial monomer. The aforementioned ethyl vinyl ether was supplied at 5mL/min with a pump while stirring the inside of the 1-liter glass-madeflask, and when 45.7 g of the ethyl vinyl ether was supplied, the pumpwas once stopped. After confirming that the temperature within the1-liter glass-made flask was raised due to the reaction, the pump wasrebooted, and the rest of the ethyl vinyl ether was supplied over 4hours. During supply of the ethyl vinyl ether, the temperature wascontrolled with a water bath such that the temperature within the1-liter glass-made flask was 25° C. After completion of supply of theentirety of ethyl vinyl ether, the stirring was further performed for 5minutes.

Subsequently, in the 1-liter glass-made flask, 10 g (mass ratio to a sumtotal of the initiator and the raw material monomer: 0.019) ofhydrotalcite (a trade name: “KYOWAAD (registered trademark) 500SH”,manufactured by Kyowa Chemical Industry Co., Ltd., a proportion ofparticles having a particle diameter of 500 μm or less: 100%, aproportion of particles having a particle diameter of 106 μm or less:94%, a proportion of particles having a particle diameter of 45 to 106μm: 56%) was added as an adsorbent and stirred at 25° C. for 1 hour,thereby adsorbing the boron trifluoride diethyl ether complex thereonto.Subsequently, the resultant was subjected to filtration to remove theadsorbent, and the solvent and the light component were removed with arotary evaporator, to obtain a crude product Bb.

The 2-liter volume SUS316L-made autoclave in which the hydrogenationcatalyst prepared in the Preparation Example had been charged wascharged with 120 g of the crude product Bb and 300 g of isooctane. Afterpurging the autoclave with hydrogen, the hydrogen pressure was kept at3.5 MPaG, the temperature was raised to 140° C. with stirring over 30minutes, and the contents were further allowed to react with each otherfor 3 hours while keeping at 140° C. After completion of the reaction,the resultant was cooled to room temperature, and the pressure wasreduced to atmospheric pressure. Filtration with a filter paper wasperformed, to remove the hydrogenation catalyst. The solvent, themoisture, and so on were removed under reduced pressure with a rotaryevaporator, to obtain a polyvinyl ether-based compound (B).

The resulting polyvinyl ether-based compound (B) was one containing 100mol % of the structural unit (b2-3) having an ethoxy group, asrepresented by the general formula (2-3), on a basis of 100 mol % of thewhole amount of structural units excluding terminal structural units.

One of the terminal structural units is the structural unit (a11-1)represented by the general formula (11-1), and in the general formula(11-1), R¹¹, R¹², and R¹³ are each a hydrogen atom, R¹⁵ is an ethylgroup, and p1 is 0.

Furthermore, the other terminal structural unit is the structural unit(a11-2) represented by the general formula (11-2), and in the generalformula (11-2), R^(11a), R^(12a), and R^(13a) are each a hydrogen atom,R^(15a) is an ethyl group, and p2 is 0.

[Examples 1 to 16 and Comparative Examples 1 to 3]

Respective components shown in the following Tables 1 to 3 were blendedto prepare refrigerator oils of respective Examples and respectiveComparative Examples, which were then evaluated according to theaforementioned evaluation methods. The obtained results are shown in thefollowing Tables 1 to 3.

The respective components shown in the following Tables 1 to 3 expressthe following compounds, respectively.

-   Component (A): PVE (A) [the polyvinyl ether-based compound (A)    synthesized in Synthesis Example 1]-   Component (B): PVE (B) [the polyvinyl ether-based compound (B)    synthesized in Synthesis Example 2]-   Component (C): Antioxidant [2,6-di-tert-butyl-4-methylphenol]-   Component (D): Acid scavenger [2-ethylhexyl glycidyl ether]-   Component (E): Extreme pressure agent [tricresyl phosphate]

TABLE 1 Unit Example 1 Example 2 Example 3 Example 4 Example 5Composition of PVE mixing ratio PVE (A) mass % 10 30 40 50 60refrigerator oil PVE (B) mass % 90 70 60 50 40 Total mass % 100.00100.00 100.00 100.00 100.00 Properties of 40° C. kinematic viscositymm²/s 64.4 61.9 65.7 63.0 65.2 PVE *1 Viscosity index (VI) — 87 81 79 7571 Characteristics Two-layer separation ° C. 53.6 54.8 56.1 58.3 62.1 ofrefrigerator temperature at the oil high-temperature side Two-layerseparation ° C. −5.2 −11.3 −23.2 −34.2 −47.8 temperature at thelow-temperature side Storage stability *2 — A A A A A ComparativeComparative Unit Example 6 Example 7 Example 1 Example 2 Composition ofPVE mixing ratio PVE (A) mass % 70 80 100  — refrigerator oil PVE (B)mass % 30 20 — 100 Total mass %   100.00   100.00   100.00 100.00Properties of 40° C. kinematic viscosity mm²/s   59.4   64.9   68.0 71.0PVE *1 Viscosity index (VI) — 67 64 57 88 Characteristics Two-layerseparation ° C.   66.4  70<  70< 51 of refrigerator temperature at theoil high-temperature side Two-layer separation ° C. −50>  −50>  −50>  −2temperature at the low-temperature side Storage stability *2 — A B C A*1: The mixture of PVE (A) and PVE (B) mixed in the mixing ratiodescribed in each Example was measured. *2: Stability after storage at−5° C. for 30 days

TABLE 2 Example Example Example Unit Example 8 Example 9 Example 10Example 11 12 13 14 Composition of Component (A): PVE (A) mass % 58.0259.4 59.22 59.04 58.92 58.62 58.62 refrigerator oil Component (B): PVE(B) mass % 38.68 39.6 39.48 39.36 39.28 39.08 39.08 Component (C):Antioxidant mass % 0.30 — 0.30 0.30 0.30 0.30 0.30 Component (D): Acidmass % 2.00 — — 0.30 0.50 1.00 2.00 scavenger Component (E): Extrememass % 1.00 1.00 1.00 1.00 1.00 1.00 — pressure agent Total mass %100.00 100.00 100.00 100.00 100.00 100.00 100.00 PVE mixing ratio PVE(A) mass % 60 60 60 60 60 60 60 PVE (B) mass % 40 40 40 40 40 40 40Characteristics Acid number after thermal mgKOH/g 0.07 1.20 1.05 0.780.56 0.22 0.01 of refrigerator oil stability test

TABLE 3 Example Example Example Comparative Unit 14 15 Example 8 16Example 3 Composition of Component (A): PVE (A) mass % 58.62 58.32 58.0257.42 — refrigerator oil Component (B): PVE (B) mass % 39.08 38.88 38.6838.28 97.70 Component (C): Antioxidant mass % 0.30 0.30 0.30 0.30 0.30Component (D): Acid mass % 2.00 2.00 2.00 2.00 2.00 scavenger Component(E): Extreme mass % — 0.50 1.00 2.00 — pressure agent Total mass %100.00 100.00 100.00 100.00 100.00 PVE mixing ratio PVE (A) mass % 60 6060 60 — PVE (B) mass % 40 40 40 40 100 Characteristics of Ring wearamount after mg 1.0 0.8 0.6 0.5 2.4 refrigerator oil lubricity test

As shown in Table 1, it was confirmed that the refrigerator oils ofExamples 1 to 7 are not only excellent in the compatibility withdifluoromethane (R32) but also favorable in the storage stability. Therefrigerator oils of Examples 8 to 16 as shown in Tables 2 and 3 areeach one containing the component (A) and the component (B) in the samemass ratio as in the refrigerator oil of Example 5 and furthercontaining at least one selected from the group consisting of thecomponent (C) to the component (E). With respect to the compatibility ofthe refrigerator oil of each of these Examples with difluoromethane(R32), it is free from any influence in the case of adding the component(C) to the component (E) to the refrigerator oil of Example 5. Forexample, the two-layer separation temperature at the high-temperatureside of the refrigerator oil of Example 8 was 66.4° C., and as for thetwo-layer separation temperature at the low-temperature side, even whenthe temperature was decreased to −50° C., no two-layer separation wascaused. In addition, the same is applicable to the storage stability,and for example, the evaluation result of the storage stability ofExample 8 was graded as “A”.

On the other hand, it was confirmed that the refrigerator oil ofComparative Example 1 was inferior in the storage stability because itdoes not contain the component (B). In addition, it was confirmed thatthe refrigerator oil of Comparative Example 2 was inferior in thecompatibility with difluoromethane (R32) at the low-temperature sidebecause it does not contain the component (A).

As shown in Tables 2 and 3, the following was confirmed from theevaluation results of each of the Examples in which the component (C) tothe component (E) were blended in the refrigerator oil having a mixingratio of the component (A) to the component (B) of 60/40 (mass ratio),while changing the blending ratio.

That is, from comparison between Examples 8 and 14 in Table 2, when theextreme pressure agent (E) is contained, there is a tendency that theacid number increases. However, as shown in Tables 2 and 3, by jointlyusing the antioxidant (C) and the acid scavenger (D), it is possible toimprove the wear resistance while suppressing the increase of the acidnumber to be caused due to the extreme pressure agent (E).

In addition, from comparison between Example 14 and Comparative Example3 in Table 3, it was confirmed that when both the component (A) and thecomponent (B) are contained, the wear resistance is more improved.

In consequence, from the viewpoint of a refrigerator oil that isespecially excellent in thermal stability, it was confirmed that arefrigerator oil in which not only the component (C) and the component(D) are contained in addition to the component (A) and the component(B), but also the content of the component (E) is small as far aspossible is preferred. In addition, from the viewpoint of obtaining arefrigerator oil that is excellent in a balance between exceptionalthermal stability and wear resistance, it was confirmed that arefrigerator oil in which in addition to the component (A) and thecomponent (B), the component (C) and the component (D) are jointly used,and a specified amount or more of the component (E) is further containedis preferred.

INDUSTRIAL APPLICABILITY

The refrigerator oil that is one embodiment of the present invention isnot only excellent in the compatibility with a refrigerant but alsofavorable in the storage stability, and therefore, it is suitably usedas a refrigerator oil to be blended in a refrigerator oil compositionusing a refrigerant. Furthermore, the refrigerator oil that is oneembodiment of the present invention is excellent in the compatibilitywith a refrigerant over a wider temperature range of from lowtemperatures to high temperatures, and therefore, it is more suitablyused as a refrigerator oil for a refrigerant containing difluoromethane(R32).

The invention claimed is:
 1. A refrigerator oil, comprising: (A) apolyvinyl ether-based compound (A) comprising a structural unit (a1)having a methoxy group in a side chain thereof in an amount of 50 mol %or more on a basis of 100 mol % of a whole amount of structural unitsexcluding a terminal structural unit in a molecular structure thereof;and (B) a polyvinyl ether-based compound (B) comprising a structuralunit (b2) represented by formula (2) in an amount of more than 50 mol %on a basis of 100 mol % of a whole amount of structural units excludinga terminal structural unit in a molecular structure thereof:

wherein: R⁵, R⁶, and R⁷ each independently represent a hydrogen atom ora hydrocarbon group having 1 or more and 8 or less carbon atoms; R⁸represents a divalent hydrocarbon group having 2 or more and 10 or lesscarbon atoms; n represents a number of 0 or more and 10 or less; and R⁹represents a hydrocarbon group having 2 or more and 10 or less carbonatoms; wherein a content ratio [(A)/(B)] of the polyvinyl ether-basedcompound (A) and the polyvinyl ether-based compound (B) is 10/90 or moreand 90/10 or less in terms of a mass ratio.
 2. The refrigerator oilaccording to claim 1, wherein the structural unit (a1) is represented byformula (1):

wherein: R¹, R², and R³ each independently represent a hydrogen atom ora hydrocarbon group having 1 or more and 8 or less carbon atoms; R⁴represents a divalent hydrocarbon group having 2 or more and 10 or lesscarbon atoms; and m represents a number of 0 or more and 10 or less. 3.The refrigerator oil according to claim 1, wherein a content of thestructural unit (a1) in the polyvinyl ether-based compound (A) is 100mol % on a basis of 100 mol % of the whole amount of the structuralunits excluding the terminal structural unit in the a molecularstructure of the polyvinyl ether-based compound (A).
 4. The refrigeratoroil according to claim 1, wherein a content of the structural unit (b2)in the polyvinyl ether-based compound (B) is 100 mol % on a basis of 100mol % of the whole amount of the structural units excluding the terminalstructural unit in a molecular structure of the polyvinyl ether-basedcompound (B).
 5. The refrigerator oil according to claim 1, wherein thestructural unit (a1) is a structural unit (a1-2) represented by thefollowing general formula (1-2):


6. The refrigerator oil according to claim 1, wherein the structuralunit (b2) is a structural unit (b2-3) represented by formula (2-3):


7. The refrigerator oil according to claim 1, wherein a total content ofthe polyvinyl ether-based compounds (A) and (B) is 70.0% by mass or moreand 100% by mass or less on a basis of 100% by mass of a whole amount ofthe refrigerator oil.
 8. The refrigerator oil according to claim 1,further comprising: (C) an antioxidant (C) in an amount of 0.1% by massor more and 5.0% by mass or less on a basis of 100% by mass of a wholeamount of the refrigerator oil.
 9. The refrigerator oil according toclaim 1, further comprising: (D) an acid scavenger (D) in an amount of0.1% by mass or more and 10.0% by mass or less on a basis of 100% bymass of a whole amount of the refrigerator oil.
 10. The refrigerator oilaccording to claim 1, further comprising: (E): an extreme pressure agent(E) in an amount of 0.1% by mass or more and 5.0% by mass or less on abasis of 100% by mass of a whole amount of the refrigerator oil.
 11. Arefrigerator oil composition, comprising the refrigerator oil of claim 1and a refrigerant.
 12. The refrigerator oil composition according toclaim 11, wherein the refrigerant is a refrigerant comprising at leastone selected from the group consisting of a fluorinated hydrocarbon, ahydrocarbon-based refrigerant, carbon dioxide, and ammonia.
 13. Therefrigerator oil composition according to claim 11, wherein therefrigerant is a refrigerant comprising difluoromethane (R32).
 14. Amethod of producing a refrigerator oil, the method comprising blendingat least: (A) a polyvinyl ether-based compound (A) comprising astructural unit (a1) having a methoxy group in a side chain thereof inan amount of 50 mol % or more on a basis of 100 mol % of a whole amountof structural units excluding a terminal structural unit in a molecularstructure thereof; and (B) a polyvinyl ether-based compound (B)comprising a structural unit (b2) represented by formula (2) in anamount of more than 50 mol % on a basis of 100 mol % of a whole amountof structural units excluding a terminal structural unit in a molecularstructure thereof, to obtain a refrigerator oil:

wherein: R⁵, R⁶, and R⁷ each independently represent a hydrogen atom ora hydrocarbon group having 1 or more and 8 or less carbon atoms; R⁸represents a divalent hydrocarbon group having 2 or more and 10 or lesscarbon atoms; n represents a number of 0 or more and 10 or less; and R⁹represents a hydrocarbon group having 2 or more and 10 or less carbonatoms wherein a content ratio [(A)/(B)] of the polyvinyl ether-basedcompound (A) and the polyvinyl ether-based compound (B) is 10/90 or moreand 90/10 or less in terms of a mass ratio.